Power connection selection apparatus

ABSTRACT

In a preferred embodiment the invention is illustrated in apparatus for improving the power factor and efficiency of a universal motor when the motor is to be used with either an alternating or direct current power source. The universal motor disclosed has a series winding, a compensating winding and an armature. The series winding and the compensating winding are connected in series with the armature. A first circuit includes a transformer having a primary winding and having the compensating winding of the motor as a secondary winding. A second circuit has the series winding and the armature connected in series. The output of a power source is sensed and connects the first circuit to the power source when alternating current is supplied, and connects the second circuit to the power source when direct current is supplied.

United States Patent 1 3,691,4 1 Hasselbach et al. 51 Sept. 12, 1972[54] POWER CONNECTION SELECTION 2,079,092 5/1937 APPARATUS Waters..318/245 Primary Examiner-Bernard A. Gilheany [72] Inventors: f R?Assistant Examiner-W. E. Duncanson, .lr.

Ohio" p o e Attorney-Myron E. Click [73] Assignees: Sel-Con,' Inc., AnnArbor, Mich.; ABSTRACT vertlfcase Ohm; In a preferred embodiment theinvention is illustrated part mterest to eac in apparatus for improvingthe power factor and effi- [22] Filed: Feb. 19, 1971 ciency of auniversal motor whenj the motor is to be v used with either analternating or irect current power [21] 116934 source. The universalmotor disclosed has a series winding, a compensating winding and anarmature. 52 us. Cl ..318/441 The Series Winding and the eempensafinswinding are 51 int. Cl. ..H02k 23/64 eenneeted in Series with thearmature A first eireu" [58] Field of Search ....31 s/-245, 441; 307/26,72, 73, includes transfwmet havihg Primary Winding and 307/128 havingthe compensating winding of the motor as a secondary winding. A secondcircuit has the series [56] References Cited winding and the armatureconnected in series. The output of a power source is sensed and connectsthe UNITED STATES PATENTS first circuit lto the power source whenalternating current is supp ied, and connects the second circuit to thepower source when direct current is supplied. 1,103,693 7/1914 Shedd..307/128 X 12 Claims, 3 Drawing Figures S LY R C E "PL I I {L2 L I?l3,Rl,l4,l4,l6,l7,lZ R I 2 W210 T p 9 H |4 T l ,fl l -.5 I Z R l C F 5 5l PB R 1 l 1 RI 1 POWER CONNECTION SELECTION APPARATUS BACKGROUND OF THEINVENTION Although a preferred embodiment of the invention will bedescribed with respect to its application and use in small appliances,specifically in an electric can opener, it is to be noted that theinventive principle and structures disclosed herein are not to beconfined to the specific use illustrated.

Small series motors are commonly designed to operate on either directcurrent or alternating current and so are called universal motors.Universal motors may either be compensated or uncompensated, the lattertype normally being used for the higher speeds and the smaller ratingsonly. Because of the reactance voltage drop, which is present inalternating currents but absent on direct current, the motor speed issomewhat lower for the same load alternating current operation,especially at high loads. On alternating current, however, the increasedsaturation of the field magnetic circuit at the crest of the sine waveof current may materially reduce the flux below the direct currentvalue, and this tends to raise the alternating current speed. It ispossible, therefore, to design small universal motors to approach thesame speed-torque performance over the operating range, for allfrequencies from zero to 60 cycles. Thus, previous compensatedtypemotors have been designed which, for example, are rated at 3,400revolutions per minute and in which the 60 cycle speed may be within 2percent of the direct current speed at full load torque, but fifteenpercent or more lower at twice normal torque. On an uncompensated motorthe speed drop will be materially greater. It is desirable though tohave almost, identical speed-torque performance from difi'erent powersupplies for some applications.

Accordingly, it is an object of this invention to provide apparatus forimproving the power factor and efiiciency of the universal motor whenthe motor is to be used with either an alternating or a direct currentpower source.

lt is a further object of this invention to provide apparatus forimproving the operation of a universal motor by providing separate motorenergizing circuits which are selected automatically in response to theconnection of the motor to a power source.

It is a still further object of this invention to provide improvedapparatus for automatically selecting proper power connections for aload when the load is to be driven by a plurality of different types ofpower sources.

SUMMARY OF THE INVENTION The aboveobjects of the invention are carriedout by apparatus which features means for automatically selecting properpower connections for a load which includes a plurality of loadenergizing circuits, means for connecting the plurality of loadenergizing circuits to a power source, and switching means forconnecting each of the plurality of load energizing circuits to a load.Means are utilized to sense one of a plurality of characteristics whicha power source may have, after the power source has been connected tothe plurality of load energizing circuits. Means responsive to thesensing means selects one of the plurality of switching means to connecta predetermined one of a plurality of load energizing circuits to theload in response to the sensing of a predetermined characteristic out ofthe plurality of possible characteristics of the power source.

The apparatus further advantageously features additional switching meansinterposed between the load and the plurality of first-mentionedswitching means to permit energization and deenergization'of a load whenone of the plurality of first-mentioned switching means has connected apower source to a selected load energizing circuit. The additionalswitching means is advantageously biased normally open to preventapplication of power to a load during operation of the sensing andselecting means.

The apparatus may further advantageously include selecting meansdesigned to open the remainder of the plurality of switching means todisable the remainder of the plurality of load energizing circuits, whenthe one of the plurality of switching means is selected and connects thepredetermined one load energizing circuit to a load.

Characteristics of the power source which may be sensed to causeselection of a predetermined load energizing circuit include whether thepower source is supplying alternating current or direct current,different magnitudes of voltage and current of different power sources,different frequencies of the power supplied by different power sources,and the like.

The apparatus may further advantageously include means for rectifying analternating current, when the load is to be driven by either alternatingcurrent or direct current, to enable application of direct current to aload whether a direct current or an alternating current power source isselected. The rectifying means may be connected between the plurality ofload energizing circuits and the load to insure the application of thesame polarity of current to the load without regard to the polarityconnections of a direct current power source to the load energizingcircuits.

Other objects, advantages, and features of this invention will becomeapparent when the following description is taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a front elevational view of an electrical appliance to whichthe teachings of this invention may be applied;

FIG. 2 is a schematic electrical circuit embodying the teachings of thisinvention and which may be utilized in the apparatus illustrated in FIG.1; and

FIG. 3 is a schematic of an electrical circuit which illustratesalternative embodiments of the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 there isillustrated an electrical appliance to which the teachings of thisinvention may formance of the can-opener at substantially the same levelwhether the applicance is connected to 110 volts alternating current or,for example, 12 volts direct current, particularly since the load torquein opening various size cans may vary substantially. It is alsodesirable to effect the greatest efficiency possible whether thecan-opener is connected to an alternating current or a direct currentsource so that the power drain on the direct current source will not beexcessive.

The can-opener 30 includes a gear wheel noted at GW which is to bedriven by the motor of this invention. A lever arm LVl is pivoted on thecan-opener 30 so that a cutting disc or wheel CW may be pivoted into andout of cutting engagement with a can rim and top which is being rotatedby the gear wheel GW. A pushbutton PB is provided on the can-opener 30and is biased in a normally open contact position so that the can-opener30 is energized only when the lever LVl is pivoted to engage the cuttingwheel CW with the can.

Referring to FIG. 2 there is illustrated a schematic circuit diagramwhich may be utilized with the canopener 30 in FIG. 1 to carry out theteachings of this invention.

It will be noted in the circuit diagrams of FIGS. 2 and 3 that numberedline diagrams have been utilized. The components can be readily locatedby reference to the line number where the component is positioned.Further, contact switching operations may be noted without designating amechanical tie between the contacts and the actuating means. Thecontacts may be located at any convenient position even though quiteremote from their actuating means. Cross reference between the actuatingmeans and its associated contacts is easily accomplished by noting inthe right-hand margin of the drawing the reference character of theactuating means, for example, R1 a relay in FIG. 1 adjacent to line 13,the line in which the relay coil R1 appears. Following the referencecharacter Rl adjacent line 13, there are noted the line numbers in whichR1 contacts close and open when caused to do so by their actuating coil,i.e., line numbers 14, 14 (since two R1 contacts appear in this line),16, 17, 17. A contact line number notation that is not underlinedindicates that those contacts are normally open as in lines 14 and 16. Acontact line number notation that is underlined indicates that thosecontacts are normally closed, i.e. as in line 17.

In FIG 2 a power source PS1 is shown in line 10, which may supply eitheralternating current or direct current. A plug PM in line 11 is a meansfor connecting-the circuit of FIG. 2 to the power source PS1 and supplypower to the circuit via leads L1 and L2. A relay coil R1 in line 13senses whether the power source is supplying alternating current ordirect current power. In the embodiment illustrated in FIG. 1 the relayR1 is a relay which is responsive to 110 volts alternating current. Thatis, if the power source PS1 is supplying 110 volts alternating currentthe relay coil R1 is energized and closes R1 contacts in line 14 and 16while opening the contacts R1 in line 17.

The closure of contacts R1 in line 14 connects an alternating currentsupply to a primary winding TPl of a transformer T1 in line 15. Asecondary winding CF of transformer T1, which is also the compensatingfield for the universal motor generally indicated at LDl, is

connected in series with a series field SF, the armature, pushbuttoncontact switch PB, and contacts R1 in line 16. Since the R1 contacts inline 16 have been closed by the energization of relay coil R1 in line 13the motor circuit is enabled for operation. Thus the movement of thelever LVl of the can-opener 30 to depress the pushbutton PBl completesthe motor energization circuit and causes the motor LDl to drive gearwheel GW to cooperate with the cutting wheel CW to open a can.

It will be noted that in a circuit of this type the switching means PBconnected between the armature and the field circuits is advantageouslynormally biased open to prevent application of any power to the motoruntil the sensing and selection operations are completed.

If the power source is, for example 12 volts DC. the relay R1 is notenergized and 12 volts DC. is connected through the normally closed backcontacts R1 in line 17. Again, upon depression of the pushbutton PB, themotor LDl is energized for operation through the series field SF and thearmature. Since the contact R1 in line 16 is not closed during directcurrent energization of the motor LDl, the compensating field CF is notincluded in the energization circuit of the motor LDl. Therefore theseries fields SF and the compensating field CF can be designed to insurethat the universal motor LDl provides substantially the same speedtorqueoutput with varying loads whether being energized by alternating currentor direct current. To this end it should be noted that it may bedesirable to supply a higher voltage to the compensating field foralternating current operation than is supplied to the series field fordirect current operation. For example if the power source is supplying12 volts direct current, then the transformer T1 may be designed so that23 volts alternating current is developed across the compensating fieldCF.

There is thus disclosed in FIG. 2 an inexpensive, highly efficientcircuit which improves the performance of a universal motor which is tobe utilized with two different types of power source. It is to be notedthat although the relay R1 has been made responsive only to alternatingcurrent, that it would be quite simple to substitute a relay which isresponsive to only direct current. If this substitution were made theclosure relationship of the R1 contacts would be reversed. That is, R1contacts in lines 14 and 16 would be normally closed and the R1 contactsin line 17 would be normally open.

A more universal circuit is illustrated in FIG. 3. A plug PL2 isprovided for connecting a plurality of load energizing circuits to aload LD2 via leads L3 and L4. A plurality of sensing units, S1 in line21 and S2 in line 22, are provided for sensing two differentcharacteristics of power supplies to which the plug PL2 may beconnected. The sensing units 81 and S2 are thus representative ofsensing units which may sense and distinguish between a number ofdifferent characteristics of different types of power supplies. As notedhereinbefore the sensing units may sense characteristics of powersupplies which may include alternating current, direct current,different magnitudes of voltage and current, different frequencies, andthe like.

For example the sensing units S1 and S2 may be utilized to sense thedifference between a 60 cycle supply frequency and a 25 supply cyclefrequency. In response to the sensing of one of the two difierentfrequencies by units S1, the S1 contacts close in lines 23 and 25 tosupply energization to a load LD2 via transformer T2 through the primaryTP2 and the secondary TS2. A back contact S1 in line 26 may be utilizedwhich opens to disable the alternate or remaining load energizingcircuit for the load LD2.

If the other of the two frequencies is sensed by the sensing unit S2 theload may be designed so that that frequency may operate the loaddirectively, thus not requiring a transformer or other translatingdevice to be inserted therebetween. However, it may be desirable 'to beable to operate the load from three different power supplies, so asecond sensing unit S2 is shown which may be used in addition to adirect connection for load energization. If the sensing unit S2 isoperated then a back contact S2 opens in line 25 to disable the firstload energizing circuit while S2 front contacts close in line 26 toenable a second load energizing circuit.

It may be desirable to design the load LD2 so that it is driven bydirect current whether the plug PL2 is connected to an alternatingcurrent source or a direct current source. Thus, a rectifier unit RF,which may include a filter, is connected between the two load energizingcircuits and the load LD2. Thus the rectifier unit RF rectifiesalternating current supplied via transformer T2 when the first loadenergizing circuit is selected. The rectifier RF as connected alsoinsures that direct current supplied via the second load energizingcircuit, when selected, will always be presented to the load LD2 withthe same polarity, without regard to the polarity of the connection ofplug PL2 to a direct currentsupply source.

By removing the transformer T2 from the circuit of FIG. 3, the circuitmay be utilized to insure that the load LD2 is properly connected to theproper one of two different magnitudes of direct current power supplies.As shown, the sensing units S1 and S2 may sense and distinguish betweenl and 220 volts alternating current. In this latter instance therectifier unit could be removed to permit load operation on alternatingcurrent.

Other modifications of the automatic power connection selection circuitof FIG. 3 will be obvious to those skilled in the art to sense thedifferent characteristics of different types of power supplies andautomatically connect the power supply to the correct load energizingcircuit to enable most efficient operation of the load.

In conclusion, it is pointed out that while the illustrated examplesconstitute practical embodiments of our invention, we do not limitourselves to the exact details shown since modifications of thesedetails may be made without departing from the spirit and scope of thisinvention.

We claim:

1. Apparatus for improving the power factor and efficiency of auniversal motor when the motor is being used with either an alternatingcurrent or a direct current power source comprising,

a. a universal motor having a series winding and a compensating winding,

b. first circuit means for supplying an alternating current to both saidcompensating winding and said series winding,

c. second circuit means for supplying direct current to said serieswinding alone,

. means for sensing the output of a power source to indicate the kind ofcurrent being supplied by the source,

e. means responsive to said sensing means for enabling said firstcircuit means when an alternating current is being supplied by a powersource and for enabling said second circuit means when alternatingcurrent is being supplied by a power source.

. Apparatus as defined in claim 1 in which a. said sensing meanscomprises relay coil means responsive only to alternating current, andin which said enabling means comprises normally open contact meansresponsive to said relay coil and connected in said first circuit, andnormally closed contact means responsive to said relay coil andconnected in said second circuit.

3. Apparatus as defined in claim 2 in which said first circuit includestransformer means having a primary winding for connection to said powersource and in which said compensating winding of said universal motoracts as a secondary winding of said transformer means.

4. Apparatus as defined in claim 2 in which said enabling means isoperative to disable the one of said first and second circuits notselected by said sensing means.

5. Apparatus for improving the power factor and efficiency of auniversal motor when the motor is to be used with either an alternatingor direct current power source comprising,

a. a universal motor having a series winding, a compensating winding andan armature,

b. said series winding and said compensating winding being connected inseries with said armature,

c. a first circuit including a transformer having a primary winding andhaving said compensating winding of said universal motor as a secondarywinding,

d. a second circuit having said series winding and said armatureconnected in series,

e. relay means for sensing an alternating current or a direct currentoutput from a power source and for connecting said first circuit to saidpower source when said power source is supplying alternating current,and for connecting said second circuit to said power source when saidpower source is supplying direct current.

. Apparatus as defined in claim 5 in which said universal motor isdriving a can-opener including a lever operated mechanism, and whichfurther includes switching means between said first and second circuitsand said armature, said switching means being biased normally open andis actuatable closed in response to said operation of said leveroperated mechanism.

7. Apparatus for automatically selecting proper power connections for aload comprising,

a. a plurality of load energizing circuits,

means for connecting said plurality of load energizing circuits to apower source,

first switching means for connecting each of said plurality of loadenergizing circuits to a load,

. means for sensing a plurality of characteristics of a second switchingmeans interposed between a load and said plurality of first-mentionedswitching means to permit energization and deenergization of a load whenone of said plurality of first-mentioned switching means has connected apower source to a selected load energizing circuit.

Apparatus as defined in claim 7 in which said additional switching meansis biased normally open to prevent application of power to a load duringoperation of said sensing and selecting means.

Apparatus for automatically selecting proper power connections for aload comprising,

a plurality of load energizing circuits,

means for connecting said plurality of load energizing circuits to apower source,

switching means for connecting each of said plurality of load energizingcircuits to a load, means for sensing a plurality of characteristics ofa power source after the power source has been connected to saidplurality of load energizing circuits, and

means for selecting one of said plurality of switching means to connecta predetermined one of said plurality of load energizing circuits to aload in response to the sensing by said sensing means of a firstpredetermined characteristic of said plurality of characteristics,

. said selecting means opening the remainder of said plurality ofswitching means to disable the remainder of said plurality of loadenergizing circuits when said one of said plurality of switching meansconnects said predetermined one load energizing circuit to a load.

10. Apparatus for automatically selecting proper power connections for aload comprising,

. means for connecting said plurality of load enera plurality of loadenergizing circuits,

. means for selecting one of said plurality of switching means toconnect a predetermined one of said plurality of load energizingcircuits to a load in response to the sensing by said sensing means of afirst predetermined characteristic of said plurality of characteristics,

said sensing means sensing the characteristics of alternating currentand direct current and distinguishing therebetween to select one of afirst and a second load energizing circuits, respectively, and

g. means for rectifying an alternating current to enable application ofdirect current to a load whichever of said first and second loadenergizing circuits are selected,

h. said rectifying means being connected between said first and secondload energizing circuits and a load to insure the application of thesame polarity of current to said load without regard to the polarityconnections of a direct current power source to said load energizingcircuits.

1 1. Apparatus for improving the power factor and efficiency of auniversal motor when the motor is being used with either an alternatingcurrent or a direct current power source comprising,

a. a universal motor having a series winding and a compensating winding,

b. first circuit means for supplying an alternating current to both saidcompensating winding and said series winding,

. second circuit means for supplying direct current to said serieswinding alone,

. means for sensing the output of a power source to indicate the kind ofcurrent being supplied by the source,

. means responsive to said sensing means for enabling said first circuitmeans when an alternating current is being supplied by a power sourceand for enabling said second circuit means when alternating current isbeing supplied by a power source, and

. switching means connected between said first and said second circuitmeans and said windings to permit selective energization of said motorafter said enabling means has selected one of said first and secondcircuits.

12. Apparatus for improving the power factor and efficiency of auniversal motor when the motor is being used with either an alternatingcurrent or a direct cur- 40 rent power source comprising,

a. a universal motor having a series winding and a compensating winding,

b. first circuit means for supplying an alternating current to both saidcompensating winding and said series winding,

. second circuit means for supplying direct current to said serieswinding alone,

. means for sensing the output of a power source to indicate the kind ofcurrent being supplied by the source,

. means responsive to said sensing means for g. said enabling meanscomprising normally open contact means responsive to said relay coil andconnected in said first circuit, and normally closed contact meansresponsive to said relay coil and connected in said second circuit, and

h. switching means connected between said first and second circuit meansand said windings, said switching means being biased in a normally openposition to prevent application of current to said windings when saidfirst and second circuits are initially connected to a power source andbefore selection of one of said first and second circuits by saidenabling means.

* w: a: a:

1. Apparatus for improving the power factor and efficiency of auniversal motor when the motor is being used with either an alternatingcurrent or a direct current power source comprising, a. a universalmotor having a series winding and a compensating winding, b. firstcircuit means for supplying an alternating current to both saidcompensating winding and said series winding, c. second circuit meansfor supplying direct current to said series winding alone, d. means forsensing the output of a power source to indicate the kind of currentbeing supplied by the source, e. means responsive to said sensing meansfor enabling said first circuit means when an alternating current isbeing supplied by a power source and for enabling said second circuitmeans when alternating current is being supplied by a power source. 2.Apparatus as defined in claim 1 in which a. said sensing means comprisesrelay coil means responsive only to alternating current, and in which b.said enabling means comprises normally open contact means responsive tosaid relay coil and connected in said first circuit, and normally closedcontact means responsive to said relay coil and connected in said secondcircuit.
 3. Apparatus as defined in claim 2 in which said first circuitincludes transformer means having a primary winding for connection tosaid power source and in which said compensating winding of saiduniversal motor acts as a secondary winding of said transformer means.4. Apparatus as defined in claim 2 in which said enabling means isoperative to disable the one of said first and second circuits notselected by said sensing means.
 5. Apparatus for improving the powerfactor and efficiency of a universal motor when the motor is to be usedwith either an alternating or direct current power source comprising, a.a universal motor having a series winding, a compensating winding and anarmature, b. said series winding and said compensating winding beingconnected in series with said armature, c. a first circuit including atransformer having a primary winding and having said compensatingwinding of said universal motor as a secondary winding, d. a secondcircuit having said series winding and said armature connectEd inseries, e. relay means for sensing an alternating current or a directcurrent output from a power source and for connecting said first circuitto said power source when said power source is supplying alternatingcurrent, and for connecting said second circuit to said power sourcewhen said power source is supplying direct current.
 6. Apparatus asdefined in claim 5 in which a. said universal motor is driving acan-opener including a lever operated mechanism, and which furtherincludes b. switching means between said first and second circuits andsaid armature, said switching means being biased normally open and isactuatable closed in response to said operation of said lever operatedmechanism.
 7. Apparatus for automatically selecting proper powerconnections for a load comprising, a. a plurality of load energizingcircuits, b. means for connecting said plurality of load energizingcircuits to a power source, c. first switching means for connecting eachof said plurality of load energizing circuits to a load, d. means forsensing a plurality of characteristics of a power source after the powersource has been connected to said plurality of load energizing circuits,e. means for selecting one of said plurality of switching means toconnect a predetermined one of said plurality of load energizingcircuits to a load in response to the sensing by said sensing means of afirst predetermined characteristic of said plurality of characteristics,and f. second switching means interposed between a load and saidplurality of first-mentioned switching means to permit energization anddeenergization of a load when one of said plurality of first-mentionedswitching means has connected a power source to a selected loadenergizing circuit.
 8. Apparatus as defined in claim 7 in which saidadditional switching means is biased normally open to preventapplication of power to a load during operation of said sensing andselecting means.
 9. Apparatus for automatically selecting proper powerconnections for a load comprising, a. a plurality of load energizingcircuits, b. means for connecting said plurality of load energizingcircuits to a power source, c. switching means for connecting each ofsaid plurality of load energizing circuits to a load, d. means forsensing a plurality of characteristics of a power source after the powersource has been connected to said plurality of load energizing circuits,and e. means for selecting one of said plurality of switching means toconnect a predetermined one of said plurality of load energizingcircuits to a load in response to the sensing by said sensing means of afirst predetermined characteristic of said plurality of characteristics,f. said selecting means opening the remainder of said plurality ofswitching means to disable the remainder of said plurality of loadenergizing circuits when said one of said plurality of switching meansconnects said predetermined one load energizing circuit to a load. 10.Apparatus for automatically selecting proper power connections for aload comprising, a. a plurality of load energizing circuits, b. meansfor connecting said plurality of load energizing circuits to a powersource, c. switching means for connecting each of said plurality of loadenergizing circuits to a load, d. means for sensing a plurality ofcharacteristics of a power source after the power source has beenconnected to said plurality of load energizing circuits, e. means forselecting one of said plurality of switching means to connect apredetermined one of said plurality of load energizing circuits to aload in response to the sensing by said sensing means of a firstpredetermined characteristic of said plurality of characteristics, f.said sensing means sensing the characteristics of alternating currentand direct current and distinguishing therebetween to select one of afirst and a second load energizing circuitS, respectively, and g. meansfor rectifying an alternating current to enable application of directcurrent to a load whichever of said first and second load energizingcircuits are selected, h. said rectifying means being connected betweensaid first and second load energizing circuits and a load to insure theapplication of the same polarity of current to said load without regardto the polarity connections of a direct current power source to saidload energizing circuits.
 11. Apparatus for improving the power factorand efficiency of a universal motor when the motor is being used witheither an alternating current or a direct current power sourcecomprising, a. a universal motor having a series winding and acompensating winding, b. first circuit means for supplying analternating current to both said compensating winding and said serieswinding, c. second circuit means for supplying direct current to saidseries winding alone, d. means for sensing the output of a power sourceto indicate the kind of current being supplied by the source, e. meansresponsive to said sensing means for enabling said first circuit meanswhen an alternating current is being supplied by a power source and forenabling said second circuit means when alternating current is beingsupplied by a power source, and f. switching means connected betweensaid first and said second circuit means and said windings to permitselective energization of said motor after said enabling means hasselected one of said first and second circuits.
 12. Apparatus forimproving the power factor and efficiency of a universal motor when themotor is being used with either an alternating current or a directcurrent power source comprising, a. a universal motor having a serieswinding and a compensating winding, b. first circuit means for supplyingan alternating current to both said compensating winding and said serieswinding, c. second circuit means for supplying direct current to saidseries winding alone, d. means for sensing the output of a power sourceto indicate the kind of current being supplied by the source, e. meansresponsive to said sensing means for enabling said first circuit meanswhen an alternating current is being supplied by a power source and forenabling said second circuit means when alternating current is beingsupplied by a power source, f. said sensing means comprising relay coilmeans responsive only to alternating current, g. said enabling meanscomprising normally open contact means responsive to said relay coil andconnected in said first circuit, and normally closed contact meansresponsive to said relay coil and connected in said second circuit, andh. switching means connected between said first and second circuit meansand said windings, said switching means being biased in a normally openposition to prevent application of current to said windings when saidfirst and second circuits are initially connected to a power source andbefore selection of one of said first and second circuits by saidenabling means.